Program / Abstract Book - KMU WWW3 Server for Education ...

No. 99 (PO 13)
Drug susceptibility test for Giardia intestinalis using WST-1 reagent
Takahiro Matsumura *,** , Tomoji Yuno * , Masaharu Tokoro **
* Department of Clinical Laboratory, Kanazawa Red Cross Hospital
** Department of Parasitology, Graduate School of Medical Science, Kanazawa University, Japan
In human giardiasis, remaining diarrhea after chemotherapy is not rare, due to low compliance with the
therapy, repeated infections or parasite resistance to administrated drugs. Actually, in some clinical
reports, the emergence of drug resistance have been suggested as a cause of treatment failure in
giardiasis, however, the method for the drug susceptibility test of Giardia intestinalis and the higher
success rate of isolation method is not yet optimized. In contrast to the field of bacteriology, such as
methicillin-resistant Staphylococcus aureus (MRSA) and penicillin-resistant Streptococcus pneumoniae
(PRSP) etc. Considering these difficult conditions of giardiasis, we have taken a challenge to establish
the metronidazole susceptibility test for G. intestinalis. Culture isolation to the axenic condition using
modified YI-S medium (consisting of a nutrient broth, vitamin mixture and serum) of G. intestinalis
was conducted using cysts excreted in patient feces, and 4 out of 6 strains were successfully isolated.
The determination of Giardia genotype was used with molecular biological analysis. Using the
well-grown clinical 3 strains (Su2: assemblage B, Su3: assemblage A, Su4: assemblage A) along with
reference strain Portland-I (PO-1: assemblage A), the metronidazole susceptibility was assessed with a
bioluminescent WST-1 cell proliferation assay (Takara: Japan). The IC50 values of PO-1 and clinical 3
isolates (Su2, Su3, Su4) were 9.36 and 9.45, 6.58, 11.72 (μM) respectively for metronidazole. Our
method could isolate both assemblage A and B, common genotypes detection from humans, and the
WST-1 reagent could confirm the drug susceptibility in the culture condition. However, some genotypes
of Giadia have been considered to be difficult to adopt axenic culture condition. So, the best culture
conditions hold the key to the assessment of the drug susceptibility for Giardia. In fact, effective drug
choices according to the results of drug susceptibility tests are general protocol in bacterial diseases, and
such a useful assessment method is now available even for giardiasis. This study might help to explain
the diversity in drug susceptibility for Giardia.
- 152 -